ysteries of the Numisphere

A denarius of Faustina Senior with an Aeternitas reverse. It is 18mm across and weighs 3.3 grammes.

This page is about one of the many mysteries that still roam free in the numisphere. Or, to put it more staidly, that still exist in the world of numismatics. It is this: what caused the hollow areas around the lettering on some Roman coins?

This might seem a very dry subject to newcomers to ancient coin collecting. But once you get hooked, you might well find that you start coming across oddities and strangenesses. Many of these have well-known explanations. Some do not. And exploring these is interesting to people with an enquiring mind.

The coin on the right illustrates the subject matter of this page ..... it is a pleasant and interesting silver denarius of Faustina Senior which is also on my halos and flow marks page. The obverse is featured there, but look now at the reverse. There are hollows around all the lettering. This looks interesting. What caused it? As far as I can discover, the answer is not known, or at least, not documented.

Scientific Approach

A methodical and scientific approach can illuminate this phenomenon. Let's examine some of the hypotheses that have been put forward, create more if possible, and test them by thinking what evidence might exist if they were true or false, and then seeing if that evidence can be found. Perhaps one of the hypotheses can then become a tested theory.

ooling – The First Hypothesis

"Tooling" is the attempt to carve away or depress some of the metal of a coin to make it look less worn than it actually is, or even to make it look like a completely different coin. Sometimes this is subtle, sometimes it is obvious. If you google "tooled ancient coins" you will come up with plenty of examples.

A tooled brass sestertius of Diva Sabina, deceased wife of Hadrian. It is 26mm across and weighs 10.0 grammes. The obverse shows Sabina veiled, and the reverse shows an altar surrounded by a laurel wreath.

A detail from the obverse of the coin shown on the left.

Would tooling be more subtle in appearance than the Faustina Senior denarius shown above? Not necessarily ... how about this for unsubtle! This "sestertius of Diva Sabina" has been extensively re-worked with some kind of machine to emphasise all the features and produce a faked texture. Some of the tooling is shown in detail on the right. This shows the area around the first A in "SABINA" on the obverse of the coin. The hollows surrounding this letter are smooth, with ridges at right-angles to the direction of the hollows. The dimples in the surface of the coin are also smooth, and I think they were made by the tip of a drill.

Further enlarged detail of part of the letter 'E' on the same coin.

Detail from the reverse of the denarius shown at the top of this page.

Here, for comparison, are two close-ups of the hollows around the lettering on the Faustina Senior coin shown above. On the left, the E and T of "AETERNITAS" on the reverse. On the right, detail around the base of the same letter E. Notice the striations in the hollows, and how different they look from the hollows on the tooled sestertius.

If this were tooling, it might:

• Be smooth-surfaced. This is not.
• Show signs of the direction the tool moved during the working. This does not.

You would NOT see:

• Any evidence inside the hollows of the surface state of the coin as it was when it was struck. And in fact on this coin there is such evidence. Inside the hollow are flow marks matching those elsewhere on the coin, which could not possibly still be there if the hollows had been made after the coin was struck.

I need go no further – this conclusively disproves the "tooling" hypothesis, at least for this coin.

unching – The Second Hypothesis

Another interesting idea is that perhaps, when making dies, individual punches were used to create the lettering. Perhaps this was not done in all periods and at all mints, but perhaps it was done often enough to create this effect. The idea is that when the punch hits the die, it pushes out metal all around it and causes the surface of the die to rise around the punch. This would then be smoothed down on most dies, but the smoothing was perhaps missed in a few cases. The raised area would then produce a corresponding hollow when the coin was struck.

This theory comes in two parts: first, that letter-shaped punches were used, and second, that this sometimes caused depressions around lettering.

How could this be detected? Well, there are many, many examples of errors in Roman coins caused by poor workmanship and careless use of the dies. What errors might you expect to find if individual punches were used in this way?

If punches in the shapes of letters caused these depressions:

• You might find examples of single letters being double-struck onto the die. This would be strong evidence. I don't know of any.
• You might see examples of different amounts of wear in the lettering on the same coin in areas which are otherwise consistently worn, caused by punches of different ages and in different states of wear, or punches being struck with different amounts of force or at different angles. There are plenty of examples of letters which are in a radically different state to the letters alongside. However, this could also easily be caused by damage or wear to the dies. In particular, partially filled dies can produce exactly this effect. So this is not conclusive.
• You might see incorrect letters corrected by overstriking onto the die with the correct one. There ARE examples of letters being corrected, which might be consistent with overstriking onto the die with a different punch. But they might also be corrections carved directly onto the die, so this is not conclusive.
• You might find examples of the use of damaged punches, resulting in uniquely malformed letters appearing, identically, on different dies. This would be conclusive, but as far as I know, there is no such evidence.
• You would not expect to find hugely obvious errors of manufacture like mirror-image letters. They would be so much more obvious, and thus avoidable, in the context of specialised work like making letter punches. But these do exist. There is one on my Unique Ancient Coins page. But this is not conclusive. Punches might just not have been in use when this coin was made.

However, there are coins which show evidence of letters being made from smaller punches of straight and curved lines, which are sometimes misaligned. But the examples I have seen do not show any depressions around the lettering.

If letter punches, or even part letter punches, caused depressions:

• You would expect to sometimes see indications of poor or hasty smoothing where the raised area on the die was smoothed away, so that toolmarks are visible. I am not aware of any examples.
• You would not expect to find two coins from the same die, both well and clearly struck, one with depressions and one without. This would be conclusive evidence that raised areas on the die, caused by letter punches or by anything else, are not the cause of these depressions. I have no examples to show, but it is worth watching out for this.

The reverse of a denarius of Vespasian. It is 17mm across and weighs 3.5 grammes.

Detail of the lettering on the denarius shown on the left.

So, I conclude that it should be easy to find good or conclusive evidence to support the use of letter punches. The evidence isn't there. But there is evidence that smaller punches were sometimes used, but not that they caused depressions around the lettering. If you find any of this evidence, please let me know!

This denarius of Vespasian shows an example of one letter being radically different from those around it: the A of the word MAX. This might be caused by a letter punch being struck very lightly into the die. But it is more probably due to the die being partially filled with waste metal. You can see that all the other letters appear to be in an identical state of wear, and it would be unlikely that one punch would be so badly worn or so poorly struck while all the others were new and consistently well struck. It is possible to find many examples of partially filled dies.

lowing – The Third Hypothesis

The metal of a coin moves and flows dramatically at the instant it is struck by the dies. Flow marks and halos are evidence of this, and there are even flow marks in the hollows around the letters on the Faustina Senior denarius at the top of this page.

When the coin is struck, metal moves into the hollows in the die. It will first bend, then flow. The lettering consists of very definite but small hollow spaces, with little or no gradation around the depths. Suppose that in some cases, metal flows into these spaces, but the gap caused by this flow does not recover, but remains hollow. Metal that has been violently distorted will gain heat, and flow more easily into the spaces in the die than the metal around it will flow to fill the gap thus caused. There will also be a strong counter-flow into the larger spaces at the centre of the die. What evidence might exist if this were the case?

If these hollows were a flow effect, you might find:

• Evidence of flow effects within the hollows. This is present – see the enlargements on this page which show very definite flow marks. The direction of these marks indicates that the stress of the flow into the centre of the die is predominant.
• Evidence of the shape of the hollows being affected by the stronger flow to the centre of the die and the position of the lettering relative to the edge of the coin. This, too, is present. See the photographs below.
• Other evidence of metal flowing when the coin is struck. This is present on some of these coins, which have strong flow marks on the obverse. These marks are caused by damage to the die which, in turn, are caused by the repeated flow of metal into the large hollow in the centre of the die.

You would not find:

• Evidence specific to the use of punches, detailed above. And this is not found.

So, the evidence in favour of this hypothesis is strong. It therefore takes on the status of a theory.

A silver denarius of Commodus. It is 18mm across and weighs 2.5 grammes. The reverse shows Salus seated.

Detail of the letter C in 'COS' on the reverse of the same denarius.

Here's another coin showing the same phenomenon. This silver denarius has hollows around some of the lettering on the reverse, but not all of it. This has only happened on the right-hand edge of the coin, where the lettering is more heavily struck, which is consistent with the "flow" theory. But you could also argue that because the whole coin is more lightly struck on one side, the part of the die that would form the hollows round the letters just did not make contact with the coin on that side. So that particular argument cannot conclusively distinguish between the "punching" and "flowing" hypotheses.

In this coin, you can see again the flow marks inside the hollow, which align with lines on the field, demonstrating the integrity of the hollows with the structure of the coin as it was struck. The contrasting striae downwards and to the right are the result of more recent damage to the coin. There is no hollowing where the shape of the letter is adjacent to the edge of the coin. This is consistent with the hollow being a flow effect, as there would be less stress and more freedom to recover at the very edge of the coin.

These hollows show some similarity to the halo effect found on many coins made in the 240s CE. There are also other similarities with those coins:

The obverse of a silver antoninianus of Gordian III. It is 22mm across and weighs 4.2 grammes.

Detail from the lettering to the right of the bust on the coin shown on the left.

Here's a pretty typical Gordian III antoninianus. These were made of a debased silver, far from pure, and the surface appearance and blurring of legend details is very typical. The lettering is often very hard to read, and unless you saw the whole thing to give context, you wouldn't easily identify the enlargement on the right as the letters F and E.

Look at the strange groove between those two letters. Clearly, the metal of the coin has reacted strongly to the stress of being struck by the die. I think that this is another form of the same hollowing that is the subject of this page. The different metal has reacted in a different way, but it is definitely describable as a depressed area by the lettering. The shape of the hollow has been very strongly affected by the general inward flow, more so than on the purer silver coins shown above, but I think the principle of its formation is likely to be the same.

This example doesn't have any flow marks in the hollow, but there is one on my Flow Marks and Halos page which certainly does. Q.E.D.

xamples elswehere on the Web

Examples of this effect can be seen on coins from Claudius I to Eudoxia, but they are easiest to find on silver coins of the Faustinas, Antoninus Pius, Marcus Aurelius and Commodus. Here are some links:

A brass sestertius of Antoninus Pius owned by Steve Niederloh.
A silver denarius of Commodus owned by Kevin Ingleston.
A silver denarius of Marcus Aurelius on Coin Archives.

redits and Disclaimers

Credit and thanks are due to Robert Kokotailo for his clear explanations of the effect on a coin when it is struck, and explanations of phenomena such as flowing, and the difference between ghosting and haloing. Also for several other illuminating observations.

Please take note that I have been examining silver coins here, and the conclusions I have drawn do not necessarily hold good for coins made from other metals, some of which also show this hollowing effect.